Signal distribution networks, particularly those employed with large signal transmission distances, (e.g. radio wave launch devices) typically contain one or more stages of amplification to ensure sufficient power levels at signal reception and recovery sites. In RF signal transmission systems, power distribution from a modulation source to the antenna emitter elements has conventionally been effected by the use of a source amplifier stage the output of which is coupled through a signal distribution network, e.g. waveguide, stripline, to one or more RF emitters. With the continuing increase in the transmitted carrier frequency and improved microwave integrated circuit devices, however, customary approaches to interfacing successive stages of a network may no longer provide an adequate means for RF and low frequency signals to be practically integrated. This is especially true of beam steering transmission type phased array antennas operating in the mm-wave or near mm-wave portion of the RF spectrum.
More particularly, because many of these antennas must be capable of scanning over large angles, constraints imposed on the generation of large grating lobes restricts the emitter element spacing typically to one-half of the free space wavelength. As a result, the integration density of microwave integrated circuit devices employed in the design of these antennas becomes increasingly higher. Where transistors and phase shifters are present, the process of incorporating both high frequency RF, D.C. power and control signals within a single scheme, which provides for large thermal dissipation (owing to the relative inefficiency of current GaAs FETs at mm-wave frequencies), becomes increasingly difficult to implement in a practical manner where the high frequency RF distribution and interfacing is concerned, dimensional tolerances of the physical structure in which the devices are contained become critical design/performance parameters. Consequently, both the length and physical characteristics of signal runs between components may significantly affect (degrade) interstage coupling/impedance characteristics of a network. Small dimensional irregularities at a signal coupling transition may influence the degree to which residual capacitance and inductance are present, causing large variations in input or output impedance at the signal coupling interface. Such constraints are especially critical in compact multielement antenna arrays, as may be employed in high performance military aircraft, where the conventional approach of using an inherently lossy branched conductor network to distribute power from single signal power source suffers unacceptable attenuation.
To obviate this drawback of substantial signal loss through the signal distribution network, antenna arrays employing monolithic integrated RF amplifier/emitter components (namely-those with the power amplifier at the emitter site by making both amplifier and antenna emitter reside within the same high speed semiconductor (GaAs) chip) have been proposed. Because of their microminiaturized circuit structure and the above-described signal transmission link limitations, the physical dimensions of signal coupling ports for interfacing such chips with other signal processing hardware have limited their incorporation in large antenna arrays. Moreover, as the density and volume of the array increases, heat dissipation, which is an especially acute requirement for GaAs FETs operating at K-band and above, becomes a significant hardware packaging consideration.